An inverter, which is adapted to convert a direct-current voltage outputted from a direct-current power supply into an alternative-current voltage and output the alternative-current voltage to a load circuit, is widely used in the field of photovoltaic power generation and wind power generation. However, a parasitic capacitance between the direct-current power supply (for example, a solar panel) and ground may produce a leakage current during operation of the inverter, which can be problematic because the leakage current would impair the quality of the outputted electric power, reduce the efficiency of the inverter, and harm the human body, thereby reducing reliability of the inverter.
Currently, inverters with various topologies such as H5, H6 and HERIC have been developed to address the problem of current leakage. However, these inverters are three-level inverter with lower efficiency. In contrast, a five-level inverter has a higher efficiency. Currently, there is an increasing interest in reducing the leakage current in the five-level inverter. For example, an existing five-level inverter is shown in FIG. 1. During operation of the five-level inverter, a power-frequency jump in a potential of a positive pole of the direct-current power supply DC, relative to a negative pole of the output, i.e. point C, may occur. The power-frequency jumping voltage, when applied across a parasitic capacitor between the positive pole (or the negative pole) of the direct-current power supply DC and ground, may produce a leakage current spike.